Deformed goldfish?

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Hi all,
I have a Ryukin that is about 9 months old (I have had him for three months). He appears to be losing ...

I have a Ryukin that is about 9 months old (I have had him for three months). He appears to be losing color on his head and his tankmate's tail started to shred. Right now they are only in a 10-gallon tank with a filter and air stone. It has been completely cycled for months now; I only wish it were bigger and we are trying to decide where we can squeeze in another, larger tank for them.

Upon closer inspection, I realized that not only is this fish losing his coloring - he is becoming transparent, not white - his mouth looks severely deformed. My other goldfish has a large mouth with distinct lips and lower jaw. This little guy, however, doesn't really have a lower jaw at all, has no lips, and his mouth stays habitually open. The opening is not much bigger than a large pinhead, whereas his tankmate could easily fit a small pea in his mouth (I don't feed him whole peas, but that was just for size comparison).

I tried to attach a photo but for now I am receiving an error message, so I hope my description is adequate.

My biggest question is this: does anyone know if this is a genetic defect, or does the discoloration have something to do with it? I also mentioned his tankmate having a tattered tail, so perhaps there is something else going on as well.

They both are fairly active, eat like pigs - the deformed one sort of sucks in his food like a vacuum cleaner - though I did just notice tonight that they seem to have long, thin, white feces trailing behind them. Is this an indication of a bacterial infection? They aren't lethargic and don't grasp at the surface for air, nor do they hide in corners or hover near the ground.

Actually, I keep my water as pristine as possible. Ammonia - 0ppm; nitrite - 0ppm; nitrate - 15ppm before my bi-weekly water change. This was why I was extremely surprised to see the fin rot.

Okay, it's permitting me to post pictures today, so here are half a dozen or so of the poor fish. The deformity is not very clear in any of them, but basically he just does not have a lower jaw. His profile actually looks similar to a great white shark rather than a goldfish, and he doesn't open and close his mouth like my other goldfish does. You can also see the discoloration on the top of his head in some of these pictures. Not sure if the two problems are related or not.

We're still working on the bigger tank...though I think we may just have to find them new homes or something because we don't really have any more room for another big tank. I really wish the LFS had told me how big they got; we would have just bought guppies or something.

*NOTE - the fish with the discoloration and deformed jaw is the same fish shown in my profile picture. Quite a difference in just a few weeks, wouldn't you say?

Tail rot on the top fish; discoloration on the head of the lower fish.

"Great White Shark" profile; no real mouth.

Here you can see the open mouth with the jaw of the fish on the left and the missing jaw of the one on the right.